The present invention relates to an optical recording medium, and is preferably applied to optical discs for example.
Until now, in optical discs, a variety of formats have been proposed as disc formats, one of which is the CAV (Constant Angular Velocity) which adopts a constant disc rotation rate. This CAV format is characterized by the capability of easily controlling the rotation of a disc, however, there are big differences in recording density between an inner circumference and an outer circumference of the disc, which has hampered an increase in the recording capacity of the disc.
In such case, in an optical disc the ZCAV (Zoned CAV) format has been employed as a format which increases recording capacity efficiently by eliminating differences in recording density between the inner and outer circumferences. This ZCAV format allows the inner circumference and the outer circumference of a disc to have the same recording density by changing the number of sectors thereon.
Therefore, in the ZCAV format, since each physical track has the different number of sectors, as can be seen in FIG. 4, when a disc is divided into a plurality of zones, pre-format headers are arranged in radial directions in each zone but are not arranged in the same radial directions over the boundary of zones (this is called xe2x80x9czone boundaryxe2x80x9d hereinafter).
FIG. 5 shows the format configuration of a pre-format header. As shown in FIG. 5, the pre-format header consists of SM (Sector Mark), which is the beginning of a sector format, VFO storing a clock to perform pull-in operation by PLL (Phase Locked Loop), AM (Address Mark) indicating the starting position of ID (Identification), ID storing a track number and a sector number, etc., and PA (Postamble) storing data for performing (1, 7) encoding.
In an optical disc device, in order to focus the spot of laser light emitted from an optical pickup on a track of the recording surface of the optical disc (that is, to perform tracking servo), a tracking error (TE) signal indicating positional information, which becomes zero (0) when the laser light is just on the track, is detected, however, when the optical pickup passes over a pre-format header, noise occurs in the tracking error signal.
In this optical disc device, tracking servo is realized by performing landing when noise occurs in the tracking error signal. For additional information, typical seek operation is divided into rough seek operation and minute seek operation, and landing is defined as an operation from the time when seek operation shifts to minute seek operation until tracking servo is performed.
In this case, as long as noise occurs in the tracking error signal periodically, the optical disc device can perform tracking servo without fail by performing landing when noise occurs.
Meantime, in the optical disc device, if the tracking pitch is made narrower to increase the recording density of an optical disc, as shown in FIG. 6, noise, which occurs when the optical pickup passes over pre-format headers (FIG. 6(A)), becomes bigger relative to the amplitude of the tracking error signal (FIG. 6(B)).
As a result, in the optical disc device, when landing is performed traversing the zone boundary, noise generated by pre-format headers arranged in a neighboring zone in the vicinity of the zone boundary occurs in the tracking error signal at a period different from that of noise generated by the pre-format headers arranged in the same zone (FIG. 6(B)), and as a result, the noise may cause tracking servo erroneously.
As shown in FIG. 7, in the recent optical disc a land-and-groove recording format in which data is recorded on both lands L and grooves G, has been employed to increase the recording capacity, wherein staggered pre-format headers are shared by the lands L and the grooves G.
In an optical disc of the land-and-groove recording format having staggered pre-format headers, as shown in FIG. 8, noise which occurs when the optical pickup passes over a pre-format header (FIG. 8(A)) becomes bigger (FIG. 8(B)) compared with the noise shown in FIG. 6(B), which has posed an inevitable problem where tracking servo is more unstable.
This problem is explained hereunder specifically. FIG. 9 shows a seek operation traversing a zone boundary. As shown in FIG. 10, when noise occurs periodically at long periods in a tracking error signal obtained when the seek operation is performed in the same zone, the optical disc device detects the noise generated in the tracking error signal when the value of the moving speed of the optical pickup becomes lower than a given threshold value, so that the detected noise causes landing and tracking servo.
As shown in FIG. 11, however, in a tracking error signal which is obtained while performing the seek operation traversing zones, when noise is generated non-periodically by the pre-format headers arranged in the vicinity of the zone boundary immediately after the occurrence of the noise which causes landing, the optical disc device is to perform the tracking servo erroneously due to non-periodically occurred noise.
That is, as shown in FIG. 12, in the tracking error signal obtained in performing seek operation shown in FIG. 13, when the optical disc device detects noise which causes landing, the tracking servo is performed when the rising or falling edge comes immediately after the noise, however, if noise occurs about the time between detection of nose and tracking servo, this noise causes tracking servo erroneously.
Also, in the optical disc, as shown in FIG. 14, there has been a problem of birefringence (distortion), or of an event in which part of pre-format headers arranged in an arbitrary zone appears in data field of the adjacent zone, resulting in the deterioration of a data error rate along the zone boundary.
As a means for avoiding such a problem of birefringence, a method to prevent the error rate from deteriorating has been employed; a few circles are provided as a buffer area along each zone boundary, and the buffer area is defined as a user-access prohibited area.
This method, however, needs to secure buffer areas including areas which are not influenced by birefringence, which makes it impossible to avoid decrease in the recording capacity.
The present invention has been made considering those points, and is intended to propose an optical recording medium capable of enhancing the stability of landing traversing a zone boundary.
In the present invention, in order to solve such problems, a recording area is divided into a plurality of zones, so that headers are arranged in radial directions in each zone but are not arranged in the same directions over the zone boundary, and the headers are arranged to be shared by the lands and the grooves. And, in an optical recording medium formatted to record data on both the lands and the grooves, headers disposed within three or more physical tracks from each boundary, thereby making it possible to prevent noise from occurring in the tracking signal during the time from the occurrence of noise, which causes landing, in the tracking error signal until the tracking servo is performed.